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Lake Almanor Cloud Seeding Project
Recent Challenges
Presented to
Weather Modification Association
April 25-27, 2012
Las Vegas, Nevada
Byron L. Marler 1, Edward F McCarthy2 and Ken Ericsson3
2
Challenges
• Concerns of a small, vocal group of citizens
• Plumas County Board of Supervisors (BOS)
• Almanor Basin Watershed Advisory Committee
(ABWAC)
• Community forum involved stakeholders
– concerned citizens
– interested citizens
– PG&E representatives
– Scientists
– public agencies
3
Concerned Citizen Perceptions – Cloud Seeding
• Chemicals = health and environmental hazards
• Non-technical interpretation of various internet
sources and personal opinions
• MSDS
• Chem-trails
• Claims of cancer clusters “in my neighborhood ---”
• Is it safe for children to play in our yards?
• We moved here for a safe, clean environment.
• And some science based questioning -- what about
nano-silver particles?
4
ABWAC FORWARDS QUESTIONS - EXAMPLES
• Chemical species released to atmosphere?
• Amount of each chemical released in operation?
• Physical and aerodynamic properties of seeds?
• Fate of seeding chemicals in air, soil and water?
• Why is the toxicity of silver iodide described differently
by MSDS sheets and by PG&E?
• Regarding Silver Iodide in Nano Form:
– Is it toxic? Status of research? Can it be inhaled?
• Provide test data (not summaries) from all studies.
5
PG&E RESPONSE
• Geochemistry and Impacts of Silver Iodide Use in Cloud
Seeding. Cardno ENTRIX report provided at ABWAC
Meeting, May 25, 2011, Chester, CA
• Responses to Questions Regarding Cloud Seeding in the
Lake Almanor Basin Updated: September 13, 2011
• Narrative vs Q/A format – specific Q/A achieved
– Lake Almanor Cloud Seeding Project
– Environmental Effects
– Air Quality
– Regulatory Setting
– Nano-particles
6
Lake Almanor -- Mount Lassen
7
Lake Almanor Cloud Seeding – operating since 1953
– Target area –
500 sq miles
above Lake
Almanor
– 10 ground-
based radio-
controlled
seeding
generators
– No aircraft
seeding
8
Lake Almanor Cloud Seeding – “Silver Iodide”
• 21.5 grams/hour/seeder
• Seeding solution is 98%
acetone.
• Each seeding particle
• 64%, 10%, 1%, 25%
• AgI 0.8 AgCl 0.2 0.005 Bi2O3 KCl = seeding salt ~ silver iodide.
• PG&E Cloud Seeding Summary 1999 – 2011
• 212 days Nov – May; 16-49 days/season; 20-93 kg; and 3 suspended seasons
• All acetone oxidized to carbon oxides, nitrogen oxides
and water vapor.
9
Environmental Effects
• Similarity in nomenclature between silver iodide and
free silver ion leads to lay-person concerns.
• Important to understand that silver iodide is used in
cloud seeding, not silver ions.
• PG&E Consultants - Cardno ENTRIX (CE) 2011
report summarized the evidence-based studies
related to cloud seeding and public health
correlations:
– no correlation between cloud seeding and public health
– Measured concentrations are typically many times safer than
the drinking water standard.
10
Environmental Effects
PG&E Response – CE 2011 Report
• Most studies of silver in the environment have
measured total silver, not the concentrations of the
individual silver species.
• Since the free silver ion is the toxic form of silver,
these studies overestimate the actual toxicity of silver
iodide, which is practically insoluble
• Seeding concentrations pose no adverse
environmental impacts
• Key References:
11
Air Quality Question – Winter Inversions
• Would cloud seeding
agents concentrate near
the ground surface
creating health
problems for those living
under these inversion
layers?
12
EPA’s AirNow website – Air Quality Index (AQI)
• AQI Categories
• Area AQI based on 8-hour
maximum ozone value Lassen
Monitoring Site and 24-hour
average PM2.5 value from the
Chester
• Based on AQI values PG&E’s
cloud seeding operations occur
during dates of satisfactory
(Good) or acceptable (Moderate)
air quality index values
Good Moderate
Unhealthy for
Sensitive
Groups
Unhealthy Very
Unhealthy Hazardous
13
Air Quality
• Cloud seeding operations are
done during windy, stormy
condition, not typically associated
with inversions.
• Cloud seeding aerosols released
during these conditions would not
concentrate near the ground nor
create health problems for the
Plumas County residents.
14
Air Quality - NSAQMD Agency Review
• NSAQMD calculated the emissions and
compared the results to the criteria for an
air permit, confirmed no permits required.
• p-dichlorobenzene was the only chemical of any
concern and NSAQMD determined the potential
emission rate of p-dichlorobenzene is 30 times lower
than trigger for a permit.
• p-dichlorobenzene is not released to the air but is
consumed by combustion, so NSAQMD’s analysis is
hypothetical
15
Materials Safety Data Sheets for Worker Safety
• MSDS are prepared by the manufacturer and lists
hazards due to ingestion, skin contact, and inhalation.
– MSDS covers the range of exposures and hazards that may
occur from manufacture to end use.
– The hazards identified are ones that could occur to workers
handling the bulk material
– The hazards identified in the MSDS do not apply to cloud
seeding related environmental levels of exposure because of
the resulting very small chemical concentrations
– MSDS cites a study on rats that required a very high intake of
silver iodide for the hazard; the cited level is the equivalent of
feeding the animal one-fourth its body weight in silver iodide.
16
Toxicity and Hazards
• Dose-Response
– All chemicals, including water, can
be toxic to humans; toxicity is determined by the dosage
(the amount of chemical applied to plant or animal).
• Important - Putting Risks/Hazards in Perspective
– The cloud seeding chemicals are shown in the MSDS as
non-carcinogenic but do potentially produce toxic effects
depending on dosage.
– How do seeding chemicals compare to other commonly used
chemicals like table salt or tooth paste in terms of relative
hazard?
17
Putting Risks/Harzards into Perspective
• National Fire Protection Association (NFPA), Hazardous
Materials Identification System (HMIS) safety ratings and lethal
dose level to 50% of test animals (LD50) are summarized in
Table A
• The MSDS for sodium fluoride indicates its potential toxic
hazards are more severe than the seeding chemicals; however,
sodium fluoride is used in very low concentrations (dosage) in
toothpaste, resulting in a non-toxic response.
• Environmental concentrations of the seeding chemicals are
extremely small (parts per trillion range) and for practical
purposes can be considered non-toxic, for the same reason as
for sodium fluoride in toothpaste (dose-response relationship).
Use Chemical Chemistry NFPA / HMIS Ratings* Lowest
LD50 **
Health Fire Reactivity (mg/kg)** Internet web link to MSDS
Cloud seeding
particles
Silver Iodide AgI 2 0 0 2820 r http://www.sciencelab.com/msds.php?
msdsId=9927257
Silver Chloride AgCl 2 0 0 5000 g http://www.sciencelab.com/msds.php?
msdsId=9927255
Bismuth Oxide Bi2O3 1/2 0 0 Not
Available
http://www.sciencelab.com/msds.php?
msdsId=9927457
Potassium Chloride
KCl 1 0 0 1500 m http://www.sciencelab.com/msds.php?
msdsId=9927402
Cloud seeding fuel
& solution –
consumed in flame
- not emitted as
this chemical to air
Acetone C3H6O 1/2 3 0 5340 m http://www.sciencelab.com/msds.php?
msdsId=9927062
p-dichlorobenze
C6H4Cl2 2 2 0 500 r http://www.sciencelab.com/msds.php?
msdsId=9923722
Propane C3H8 1/0 4 0 Asphyxiant www.amerigas.com/pdfs/safe_eng.pdf
Table salt Sodium Chloride
NaCl 1 0 0 4000 r http://www.sciencelab.com/msds.php?
msdsId=9927593
Toothpaste
ingredient
Sodium Fluoride
NaF 3/2 0 0 52 r http://www.sciencelab.com/msds.php?
msdsId=9927595
Food ingredient Caffine C8H10N4O2 2 1 0 127 m http://www.sciencelab.com/msds.php?
msdsId=9927475
Medicine Asprin C9H8O4 2 1 0 200 r http://www.sciencelab.com/msds.php?
msdsId=9922977
Food ingredient Vitamin D3 C27H44O 3 1 0 42 r http://www.sciencelab.com/msds.php?
msdsId=9923455
* NFPA ratings are shown; / HMIS shown if different from NFPA; number hazard ratings; larger numbers indicate greater hazard
** Toxin weight / kilogram of body weight; test animal rat - r, mouse- m, guinea pig – g; smaller numbers imply greater toxicity
All chemicals produce hazards at high concentrations (dosages); for example, all chemicals in this table can produce tissue
(skin, eyes, respiratory, etc.) irritation.
TABLE A - MSDS Summary
19
Nanoparticles – Particle dimension less than 100
nanometers
• 100 nanometers = 0.1 micron
• Cloud seeding particles (0.05 – 0.1 micron) are nano
• USEPA is evaluating the toxicity of nanosilver as
applied in consumer goods
– clothing, medical equipment, shampoo, toothpaste,
nutritional supplements, ---
– focus of EPA review - use of the antimicrobial form
of silver (silver ion) as nanoparticles
20
Nanoparticles
• Engineered nanosilver - specifically made to be
predominantly the ionic form of silver, which is the
effective anti-microbial agent.
• Cloud seeding particles are not engineered nanosilver.
• Nanoparticles produced by cloud seeding are silver
iodide particles, which do not have the anti-microbial
effects of engineered ionic silver nanoparticles.
21
Nanoparticle Regulation
• Air quality regulations for particulate matter -
10 micron (fine) and 2.5 micron (fine) size.
• Nanoparticles (ultrafine) fall within both categories.
• The emission amount from cloud seeding is far less
than the triggers for permits controlling emissions of
fine particles.
• Engineered nanoparticles, are being considered for
regulation by the USEPA.
22
USEPA Recommends Further Research
• Effects of engineered silver nanoparticles on humans
• Uncertainty is that engineered nanoparticles of
elemental or ionic silver can penetrate cell walls,
whereas the larger elemental or ionic silver does not.
• The USEPA (2010 a) notes that silver iodide is used
for cloud seeding, but the recommended studies do
not extend to the combustion-related formation of
nano-sized particles of silver iodide.
• Silver iodide retains its composition – negligible
ionization in environment.
• Research summarized in Cardno ENTRIX, 2011
23
OUTCOME – ABWAC Reports
• “There’s no evidence that cloud seeding has
negative effects on the environment or public health.
But more research should be done.”
• Recommends
• Assure cloud seeding installations located in Plumas County are secure,
including all chemicals stored on site.
• Inform the county of any proposed changes to current cloud seeding programs.
• Work with PG&E science staff and outside experts in the fields of ecotoxicology,
atmospheric chemistry and nano-technology to develop a rigorous monitoring
program.
• Include silver as a monitored constituent as part of the long-term water quality
monitoring of Lake Almanor.
• Use a website to provide real-time notice of when cloud seeding activities are
occurring, as well as cloud seeding activities to date.